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language
jpn
Title Transcription
セイナン ニホン ノ マイヅル ソウ グン ノ チキュウ カガクテキ ケントウ トクニ チュウ ジョウブ ペルム ケイ キョウカイ ニ オケル ソセイヘンカ ニ ツイテ
Title Alternative (English)
Geochemistry of Maizuru Group, Southwest Japan : Compositional changes across the Middle-Upper Permian boundary
Author
Dozen, Kaori Department of Geology, Faculty of Science, Shimane University
Musashino, Makoto Department of Earth Sciences, Kyoto University of Education
Description
西南日本の舞鶴帯は細長い堆積盆地を形成しており,厚い黒色泥岩の堆積が行われた.本論では中・上部ペルム系の境界を挟んでの地球化学的特徴の変化を検討した.舞鶴層群の泥岩の地球化学的検討からそのprovenanceは成熟した島弧や大陸縁辺が予想される.舞鶴層群は一般にPAAS(post-Archean Australian shales)と類似の組成を示す.そして,アルカリ元素の中ではKやRbに比べてNaやCsに富んでいる.希土類については一般的にEuの負異常が見られ,軽希土類よりも重希土類の濃集がみられる.有機炭素濃度は1%以下で低いが,C/N比やN/P比は海棲生物のそれを代表するレッドフイールド比と類似する.有機炭素量やその他の元素についての明瞭な変化が中・上部ペルム系境界の下位の層準でみとめられる.ここでは,イオウの濃集,有機炭素,窒素の減少,Th/U比,V/(V+Ni)比の減少,As, Sbの濃集がともなわれる.また,この層準において,Naが濃集し,Euは他の層準に比べより明瞭な負異常を示すとともに,Cs, Rb, Kなどは減少する.中/上部境界の下位におけるこのような変化は,火山活動にともなう過剰の栄養塩の供給による基礎生産の高まりが起こったと予想される.そして,有機物の分解によって堆積盆地が還元的環境へ変化し,引き続いて放散虫生産量の衰退が生じたと考えられる.
Description Alternative
Voluminous black mudstone deposition occurred in the narrow and elongated Maizuru Belt of Southwest Japan during the Permian. Geochemistry of these mudstones reflects the provenance of the Maizuru Belt across the Middle and Upper Permian boundary. Proposed provenance of the mudstones suggests derivation from a mature island arc or continental arc. Mudstones of the Maizuru Group show similar composition to PAAS (post-Archean Australian shales), but are enriched in Na and Cs, and other alkaline elements (K, Rb). Among the rare earth elements (REE), negative Eu anomaly is common in samples, and heavy REE are enriched rather than light REE. Although organic carbon contents are less than 1 wt%, the ratios C/N and N/P coincide with Red-fields ratio for marine planktonic organisms. Abrupt change in chemistry occurred at the Middle and Upper Permian boundary with high concentration of sulfur, As and Sb, and depletion in organic carbon and nitrogen, and lower ratio of Th/U and V/(V+Ni). This corresponds to enrichment in Na, and depletion in Eu, Cs, Rb and K. The environmental change across the boundary may be caused by active volcanism, which resulted in an anoxic basin with consequent decline in radiolarian productivity.
Subject
Geochemistry
Maizuru Group
Permian
major and trace elements
REE
anoxia
Redfields ratio
primary production
Southwest Japan
Journal Title
Earth Science (Chikyu Kagaku)
Volume
50
Issue
2
Start Page
125
End Page
137
ISSN
0366-6611
ISSN(Online)
2189-7212
Published Date
1996-3-25
DOI
Publisher
地学団体研究会
Publisher Transcription
チガク ダンタイ ケンキュウカイ
Publisher Aalternative
The Association for the Geological Collaboration in Japan
NII Type
Journal Article
OAI-PMH Set
Faculty of Science and Engineering